Heating and ventilating system



Oct. 20, 1936. R. J. PARSONS HEATING AND VENTILATING SYSTEM INVENTOR.

Patented Oct. zoybo I t 2,058,252

UNIT-ED STATES PATENT orricl:

aosazsz HEATING' Asn vanmnrmo srs'raiu Robert J. Parsons, Schenectady, N. Y., assigner to Consolidated Car-Heating Company, Inc., Albany, Ne Y., a corporation ci' New York Application February 21, 193s, semi No. asu

s claims. (ci. 21o-zo) 'I'his invention relates to electric railways, grammatic or schematic view of a device which particularly to the electric cars used thereon may be added to the arrangement of Fig. 1 as an and more especially to the heating and ventilatl additional auxiliary or supplementary feature: ing of such cars. Fig. 3 ls a schematic view of another auxiliary,

5 A. principal object of this invention is to acadditional or supplementary feature which' may 5 complish the heating and Ventilating of a car be added .to the system of Fig. l; Fig. 4 is a of the type specified by an expenditure of a detail view illustrating schematically the conn minimum amount of electrical energy. f struction of a valve used in the system of Fig. l.

A further object oi the invention is to provide In the drawing numeral, l indicates an air l0 a system for heating and Ventilating a car of duct or conduit. One end 2 of this conduit l0 the type specified which will bepracticaliy autcopens into the passenger space of an electric matic in operatiom to the end that it `not only car. Ot courseit is to be understood that the will not require manual operation, which may view is diagrammatic or schematic and the at times be. unfortunately lacking, but it will showing is merely for the'purpose of illustraserve, as near as is possible, to maintain the tion and applicant, oi' course. does not mean to 15 heating and Ventilating of the car normal, under exclude the connection of the conduit end 2 to diverse weather conditions oi heating and venany suitable distribution system such as is comtilating. I mon or usual in connection with the heating and A further object oi the invention is to provide Ventilating of electric cars as'it is common praca system of heating and Ventilating i'ora car tice to have a Ventilating and heating conduit 20 of the type described which will operate on the extend lengthwise of. the car upon each side principle of a plenum system during the time with openings at intervals for allowing ingress when' heating of the car is required and will act and egress for the heating and Ventilating meupon the principle of an exhaust system during dium;

s, the time when no heat is reqinred, but ventlat- 'The end 3 of the conduit may likewise be con ing is necessary. sidered as opening into the heating and ventilat A further object of the invention is the pro ing space of an electric car and as opening duction of a system having the advantages and therein in any of the usual orwell known man. for the purposes speciiied which will he *so denh ners or positions. v

:to ble as to be readily adaptable to the diverse conn End t oi' theconduit opens to the outside air. m ditions likely to be found in commercial prao-1 rrlisis opening may be arranged at anyplace and tice. any usual manner customary in connection .A further object of the invention is the pro with the heating and Ventilating of electric cars duction of a system or" the type described which or similar structures.

se will loe composed @i relatively Slmpie apparatus. in order to secure a circulation of air within easy to install and maintain and substantially the conduit i and so within the car, applicant free from delicate parts likely to get out of t prefers a-power driven fan or air propeller, and order and to require attention even at substanpreferably one of the electric type most aptially wide intervals. propriately mounted within the conduit i. Such 40 Other Objects and advntages' Will appear as an air propeller or draft creator is indicated at 40' the description of the particular physical embodi- 5 as an ordinary electric motor driving a ian ment selectedtoillustrate the invention progresses blade 6. This motor 5 is conveniently driven and the novel features Will be particularly from electrical energy-taken from the trolley. pointed out in the appended claims. In order to furnish heat to the air which is In describing' the invention in detail and the propelled through the conduit l., applicant in- 5 particular embodiment selected to illustrate the stallsthe ordinary and well known traction moinvention, reference will be had to the accomtor resistors it in position to have the moving panying drawing and the characters oi' refer= air pass thereover, as in the conduit l.

ence thereon wherein like characters of refer- As the traction motor resistors l0 may not at ence designate like parts throughout the several times supply suiiicient heat to heat adequately w views, and in which: the air owng through the duct l and out of the Figure 1 is a diagrammatic or schematic iliusend 2, applicant has made provision for further tration o: a heating and Ventilating 'system for heating the moving air in duct i. This preferan electric car operable upon an electric railway ably takes the form of electrically energized re embodying applicants invention; Fig. 2 is a dief sisters positioned so that the air flowing through duct I must pass thereover. It is usual and customary to supply electrically energized resistor heaters for such purposes, and it is usual to either concentrate or distribute them in accordance with what seems to be the best construction, but i'or the purposes ot illustration applicant has concentrated or assembled the heaters at one point within the duct I. These resistor heaters are indicated by II and are energized, as will be more fully hereinafter described, by electrical energy from a trolley T.

As applicant desires not only to heat the car but also to ventilate it, it is impossible to merely recirculate the air in the car and to the end that proper ventilation may be secured when desired, applicant has provided not only the entrance opening 3 communicating with the passenger space of the car but also the entrance opening I communicating with the outside atmosphere.

With all o! the parts as shown in the position as illustrated by Fig. l, the fan i would draw air not only from the passenger space oi the car but also from the outside atmosphere and passing over the traction motor resistors Ill would be heated so that approximately one half of the air circulating through the car would be recirculated air and the other hal! would be frh air. 'This would be the condition if the interior ot the car was at a temperature say below 55 F. and above 50 F., the limits assumed by applicant ior the two main thermostats positioned within the passenger space oi' the car for regulating the automatic operation of the system. The thermostat under the above stated conditions which is above 50 is the thermostat II and the thermostat which is below 55 is the thermostat I2. each of which is represented in the conventional manner as being of the ordinary sylphon form. Under the conditions as stated, that is, with the temperature in the passenger space of the car above 50 the thermostat II' would be closing contact between the members Il and I4 and with the temperature below 55 the thermostat I2 would be closing contact between the members I5 and I B so that, as will be more fully hereinafter described, both solenoids I1 and I8 would be de-energized and no air would be supplied to the system which controls the dampers Il and 2l so that they would be in position as shown in Fig. i.

It is also to be observed that under the conditions specified even when manually operable switch 1I closes upon contact .22 no electrical energy would be supplied to the auxiliary or supplementary heating resistors or heaters II.

If the temperature in the passenger space of the car falls below the thermostat Il' will break the connection between members Il and Il so that with manuallyoperable switch Il in contact with contact 22 electrical energy will iiow from the member 'Il to and through electro-magnet or relay 23 and cause its amature Il toberaisedintocontactwithwirelisothat electrical energy may then iiow from 1I through wire,armature2l,wires20and21toand through all ot the resistors II thereby heating the same and furnishing additional heat to the resistors Il to the current of air flowing through conduit I, thereby more strongly and quickly heating the passenger space of the car. Y

In order to more quickly and emciently heat the passenger space ot the car under the conditions assumed. that is. in'which thermostat II' is exposed to a temperature less than 50 not only would the resistors Il be heated but the damper I8 would be shifted to the dotted line position as shown in the figure. This would be done sof-hat while heating the car when its is below 50 there would be no air taken from the outside. In order to shii't the damper Il to the l dotted lino position it is pivoted at Il and is connected at 29 to the piston rod III of a piston II in an air cylinder 32. This piston li is normally spring pressed by the spring u to the position as shown in Fig. 1. When the thermostat Il' is exposed to a temperature less than 50 the electromagnet 23 is energized as hereinbeiore stated and the armature 2| is raised thereby energizing electro-magnet or valve I 1, the current iiows in a circuit as follows: 10. wire 2l,` armature 2l. wire 2B, resistance 3l, wire II, electro-magnet coil I1, and wire I6 to ground or common. When electro-magnet I1 is energized the valve I1 is raised allowing compressed air entering at the end 38 of the pipe to ilow to the valve 30, shown in detail in Fig. 4. This valve has a plug Il therein which moves to the position as shown in Fig. 4 when air enters through the pipe Il. 'I'he eiect of this is to close oi! the pipe 42 to the entrance of compressed rair but allow the compressed air to flow into the pipe I8. 'I'he air owing through the pipe 4I causes the piston Il to be raised, as viewed in Fig. 1, thereby causing damper I8 to be moved to the dotted line position.

When damper I! is in the dotted line position, and resistors Il are energized, the heating oi' the passenger space of the car is most rapid and eilicient, because all of the air forced into the car through the duct I is taken from the passenger space oi' the car through the entrance l so that it is practically a recirculation of the air in the car.

When the temperature of the space in car has been raised from below 50 to 50, the thermostat Il' makes contact between members Il and Il and so by-passes the electro-magnet 2l, thereby de-energlzing it and causing amature Il to break circuit with wire 25. This removes the heating energy from the resistors I I and de-energiaes electro-magnet I1 thereby causing valve Il to seat and prevent the entrance od compressed air under the piston 3| so that the spring 3l gradually pushes the piston to the position as shown in Fig. l and the damper Il to the position as shown in Fig. l. Continued operation of the t A l under the conditions last outlined will cause a further heating ot the car because o! the heating of the moving air by the traction motor resistors Il, but not only will heating be accomplished, but ventilation as well because the entrance I to the duct I is also open and part of the air driven into the car will be taken from the car and part from the outside atmosphere.

When the temperature of the car goes above the thermostat I2 will break contact between Il and Il so that the by-pass around electromagnet Il will be broken. Electro-magnet Il will be energized by current nowing in a path as follows: 1l, manually operable switch Il, wires and Il, electro-magnet Il and wire Il to ground or common. Current ilowing in the above traced path energlles theelectro-magnet Il and causesthevalve Iltoberalsediromitsseatthereby allowing compressed air to iiow in at the end l! oi the pipe il. The air iiowing in the pipe Il will pass into pipe l! and move the valve I to the left, as viewed in Fig. 4, stopping the end oi' pipe II but allowing the air to ilow into the pipe 43 where it will operate the damper Il to the dotted line position. At the same time, the air will flow 76 into pipe 5I and under piston 52 in cylinder 53, causing the piston rod 54 to raise the damper 20 to the dotted line position as shownin Fig. l. The conditions last described the'heating of the passenger space of the car will be aiected by the air which passes over traction motor resistors Ill4 a portion is returned as is represented by the i volume which gets by the space between the upper end of the Vdamper 2li in the dotted line position and the wall of the conduit I. As a consequence the system is working practically as an exhaust system. The air is being drawn from the passenger space of the car and only partly replaced, asa consequence,k some air must reach the passenger space of the car through the doors or windows or other available entrance. This last described arrangement of the several parts is the one which will be in force when no heat is called for by the car thermostat I2. The damper 20 will be adjusted so that the amount of heat passing by will be sufficient to maintain the car temperature during average operating conditions. It causes the Ventilating and heating of the passenger space of the car with the minimum expenditure of electrical energy. `This will be seen to be so when it is realized that the heating is done entirely by the traction motor resistors which furnish what is practicallywaste heat, and the only energy necessary to be expended for the Ventilating and heating is that required to operate the fan motor 5. It is to be observed, however, that the method of heating which contemplates a usual condition wherein all of the heat is supplied by the traction motor resistors I is especially applicable to those situations where the traction motor and its circuits are arranged not only so that the resistors are in circuit as is customary upon accelerating but are also in circuit with the motors when decelerating, that is, the motors are used as a dynamic brake to retard the motion of the car. The amount of heat generated in the resistors Ill when used in connection with a motor used as a dynamic brake is such that an ample supply of heat is secured from the resistors alone to enable the passengerv space of the car to be suitably heated under generally existing conditions willie the car is in operation.

As will be readily understood, if the system is in the condition whereby damper I9 is in the dotted line position and damper 20 is in the dotted line position with electro-magnet I8 energized because the temperature in the passenger space of the car is greater than 55, then when the temperature falls to 55 or lower, the members Iand I5 would be conductively united estabiishirig a by-pass or shunt around the electromagnet I8 thereby de-energizing it. The deenerglzation of electro-magnet I8 would remove the air` pressure from pipes 42 and 5I and so cause damper 2U to go to its full line position and damper I9 to its full line position so that the operation of the system would then proceed ashereinbefore described.

AIf afterdampers I9 and 20 are returned to the inbefore described, and break the shunt around electro-magnet 23.

It is vitally necessary that the resistors II! do not overheat. To this end applicant has positioned a thermostat 55, so as to be affected by them or the air passing thereover. It thermostat 55 is exposed to too great a heat contact is broken between 5B and 51 so that electro-magnet 58 becomes de-energized as this electro-magnet is in a circuit as follows: trolley T, manually operable switch 59, resistance 60, wire 5l, electro-magnet 58, wire 62, contact 55, thermostat 55, contact 51, and wire G3 to common or ground. When the electro-magnet 58 is de-energized its armature 54 falls thereby de-energizing main circuit breaker 55 of the car, the circuit of which is as follows: trolley T, wire 66, electro-magnet or circuit breaker 65, wire 51, armature 6I, and wire B8 to common or ground. When electro-magnet circuit breaker 65 is de-energized the armature 69 breaks contact with the general current supply 'l0 of the car from the trolley T.

If too much heat is generated by the resistors I0 the thermostat 55 controlling the circuits and apparatus described will cause the main circuit breaker 65 of the car to open thereby cutting off all energy, as is usual, from the resistors I0.

It is essential that the motor 5 is always operating while the resistors Il) are functioning. To this end the circuit of the motor 5 originates on a manually operable switch 'l which not only places the motor 5 in connection with electrical energy but also places the traction motors control circuits through wire 9 in connection with the electrical energy. By this means it is certain that motor 5 is always supplied with energy for the operation thereof when it is positioned to heat resistors I0 by the operation of the traction motors.

In Fig.. 2 an auxiliary or supplementary means are shown which may be used with the arrangement as shown in Fig. l. In this arrangement one portion of thermostat 'II is positioned adjacent the resistors I0 and another portion of the thermostat, the expansible and contractible member l2 is positioned outside `of the duct I and has an operating rod 'I3 attached thereto cooperating with a damper 14 pivoted at l5. When the temperature of the air passing over 'Il reaches a.eertain low limit, say 55, the sylphon member i12 `*will have allowed the damper 14 to open to the position as shown in full lines in Fig. 2 and at the same time the damper I9 will have been moved to the dotted line position as shown in Fig. 2 so that not only is no air being taken from the outside atmosphere through the entrance 4 but all of the alrmoved by the fan 6 is not passing over the resistors IIl as part of it is ilowing out through the opening i6 uncovered by v damper. '14,y so that the remaining volume of air being less becomes more greatly heated in passing over the resistors I0. When it becomes so greatlly heated that it raises the temperature 'II beyond, say, 55", then the sylphon 12 through the rod 'I3 closes the damper 14 and opens the damper i8 and the system proceeds in the normal manner.

Another method of providing for a reduced temperature of the air passingover resistors Ill is shown in Fig. 3. Just before reaching resistor II the air is passed over sylphon 11 which as the temperature lowers gradually raises the damper 18 pivted atv 'I9 lso that it decreases the available area of duct I, consequently decreases the volume of air passing therethrough and so the volume oi air passing over resistors i0. As a consequence, the air which passes over the resistors lli becomes more intensely heated and as it becomes more intensely heated causes the damper 6 'il to gradually move to its full line position as shown in Fig. 3.

From the hereinbeiore given description, it will now be understood that applicants system of heating and Ventilating an electromotor operated car is such that it operates as a plenum system when heating is required in that it forces heated air into the space to be heated, and as an exhaust system when ventilation only is required, as at that time more air in volume is drawn out of the car than is returned thereto by the heating and ventilating duct l so that some air must leak in from available openings in the car.

Having'described the principle and mode of operation of my invention and one particular physical embodiment thereof, it is desired to have it understood that the particular form described is illustrative merely but does not exhaust the possible physical embodiments oi' the idea of means underlying the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a car heating system, in combination: a duct adapted for the passage of air therethrough. provided with a discharge opening communicating with a space to be heated, an inlet opening vcommunicating with the space to be heated, and an inlet opening communicating with the outside atmosphere; an electrically driven air propeller positioned to'discharge air through the discharge opening and to draw air 4into the duct through the inlet openings; traction motor resistors positioned in .the duct between the air propelling means and the discharge opening thereof; supplementary electrically energizable heating resistors situated within the air duct in such position that all air leaving the discharge opening of the air duct must pass thereover; means for supplying energy to 45 the supplementary resistors governed by the temperature of the space to be heated; a damper, said damper provided with a pivot and so positioned that the damper may close or open the entrance to the duct from the outside at- 60 mosphere; means governed by the temperature within the space to be heated to control the movement of the said damper whereby the entrance to the duct from the outside atmosphere is closed when the temperature of the space to lilil be heated is below a predetermined minimum.

2. In a car heating system, in combination: a duct adapted for the passage oi' air therethrough, provided with a discharge opening communicating with a space to be heated, an inlet opening 60 communicating with the space to be heated, and

an inlet opening communicating with` the outside atmosphere; an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct 06 through the inlet openings; traction motor re-` o 70 such position that all air leaving the discharge opening of the lair duct must pass thereover; means for supplying energy to the supplementary resistors governed by the temperature of the space to be heated; a damper, said damper u. provided with a pivot and so positioned that the damper may close or open the entrance to the duct from the outside atmosphere; means governed by the temperature within the space to be heated to control the movement of the said damper whereby the entrance to the duct from the outside atmosphere is closed when the temperature of the space to be heated is below a predetermined minimum; said duct provided with an opening to the outside atmosphere beyond the traction motor resistors in the direction toward the discharge opening of the duct; a damper mounted to pivot to cover and uncover said opening, said damper when open partially closing the air duct whereby a less volume of air can be propelled by the air propeller past the damper toward the discharge opening oi' the duct, said last mentioned damper when unclosing the opening allowing a portion of the air propelled by the air propeller to iiow to the outside atmosphere whereby a greater volume of air is withdrawn from the space to be heated than is delivered thereto; and means governed by a maximum temperature of the space to be heated for controlling the operation oi' the last mentioned damper.

3. In a car heating system, in combination: a duct adapted for the passage of air therethrough, provided with a discharge opening communicating with aspace to be heated, an inlet opening communicating with the space to be heated, and an inlet opening communicating with the outside atmosphere; -an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct between the air propelling means and the discharge opening thereof; supplementary electrically energizable heating resistors situated within the air duct in such position that all air leaving the discharge opening of the air duct must pass thereover; a thermostat positioned in the space to be heated; means governed by `the thermostat for supplying .energy to the supplementary resistors; a damper, said damper adapted to. be movable and to be positioned to open or close the entrance to the duct from the outside atmosphere; means controlled by the thermostat for causing said damper to open or close the entrance to the duct from the outside whereby the entrance to the duct from the outside atmosphere is closed by the damper when the supplementary resistors are energized.

4. In a car heating system, in combination: a

yduct adapted for the passage of air therethrough,

provided with a discharge openingcommunicating with a space to be heated, an inlet opening communicating with the space to be heated, and

an inlet opening communicating with the outside` atmosphere; an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct between the air propelling means and the discharge opening thereof; supplementary electrically energimble heating resistors situated within the air duct in such position that all air leaving the discharge opening oi the air duct must pass thereover; a damper, said damper adapted to ,close or open the entrance t0 the duct from the outside atmosphere; said duct provided .with a second discharge opening positioned between the traction motor resistors and the supplementary resistors; a damper adapted ing and when open to partially close the duct; a thermostat positioned in a space to be heated; means controlled by the last mentioned thermostat when the temperature of the space to be heated is above a predetermined maximum for causing the first mentioned damper to close the entrance to the duct from the outside atmosphere and to open the discharge opening to the outside atmosphere whereby the system acts as an exhaust system and the space to be heated receives additional air from the outside atmosphere through any available openings.

5. In a car heating'system, in combination: a duct adapted for the passage of air therethrough, provided with a discharge opening communicative with the space to be heated, an inlet opening communicating with the space to be heated, and

an inlet opening communicating with the outside atmosphere; an ele'ctrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct between the air propelling means and the discharge opening thereof; supplementary electrically energizable heating resistors situated within the air duct in such position that all air leaving the discharge opening of the air duct must pass thereover; means for supplying energy to the supplementary resistors governed by the temperature of the space to be treated; a damper, said damper provided with a pivot and so positioned that the damper may close or open the entrance to the duct from the outside atmosphere; and means to control the movement of the damper whereby the entrance to the duct from the outside atmosphere may be closed and opened selectively.

6. In a car heating system, in combination: a duct adapted for the passage of air therethrough, provided with a discharge opening communicating with a space to be heated, an inlet opening communicating with the space to be heated, and an inlet opening communicating with the outside atmosphere; an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct between the air-propelling means and the discharge opening thereof; supplementary electrically energizable heating resistors situated within the air duct in such position that all air leaving the discharge opening of the air duct must pass thereover; means for supplying energy to the supplementary resistors governed by the temperature of the space to be heated; said duct provided withv an opening to i the outside atmosphere beyond the traction motor resistors inthe direction toward the discharge opening of the duct; a damper mounted to pivot to cover and uncover said opening, said damper being movable to control the volume of air propelledvby the air propeller past the damper toward the discharge opening of the duct, said damper when unclosing the opening allowing a portion of the air propelled by the air propeller to ilow to the outside atmosphere whereby a greater volume of air is withdrawn from the space to be heated than is delivered thereto; and means governed by a maximum temperature of the space to be heated for controlling the operation of the damper.

7. In a car heating system, in combination: a duct adapted for .the passage of air therethrough, provided with a discharge opening communicating with a space to be heated, an inlet opening communicating with the space to be heated, and an inlet opening communicating with the outside atmosphere; an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct between the airpropelling means and the discharge opening thereof; supplementary electrically energizable heating resistors situated within the air duct in such position that all air leaving the discharge opening of the air duct must'pass thereover; means for supplying energy to the supplementary resistors governed by the temperature of the space to be heated; a damper, said damper provided with a pivot and so positioned that the damper may close or open the entrance to the duct from the outside atmosphere; means governed by the temperature within the space to be heated to control the movement of the said damper whereby the' entrance to the duct from the outside atmosphere is closed when the temperature of the space to be heated is below a predetermined minimum; said duct provided with an opening to the outside atmosphere beyond the traction motor resistors in the direction toward the discharge opening of the duct; a damper mounted to pivot to cover and uncover said opening, said damper being movable to control the volume of air propelled by the air propeller past the damper toward the discharge opening of the duct, said last named damper when unclosing the opening allowing a portion of the air propelled by the air propeller to flow to the outside atmosphere whereby a greater volume of air is withdrawn from the space to be heated than is delivered thereto; and means governed by a maximum temperature of the space to be heated for controlling the operation of the last mentioned damper. c

8. In a car heating system, in combination: a duct adapted for the passage of air therethrough y'provided with a discharge opening communicating with a space to be heated, an inlet opening communicating with the space to be heated, and an inlet opening communicating with the outside atmosphere; an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct between the air propelling means and the discharge opening thereof; supplementary electrically energizable heating resistors situated Within the air duct in such position that all air leaving the discharge opening of the air duct must pass thereover; said duct provided with a second discharge opening positioned beyond the traction motor resistors in the direction toward the discharge opening of the duct; a damper adapted to close and open selectively the lastnamedopening to control discharge of air from the duct to the outside atmosphere, and means to operate said last-named damper.

9. In a Icar heating system, in combination: a duct adapted for the passage of air therethrough, provided with a discharge opening comrnunicating with a space to be heated, an inlet opening communicating with the space to be heated, and an inlet opening communicating with the outside atmosphere; an electrically driven air propeller positioned to discharge air through the discharge opening and to draw air into the duct through the inlet openings; traction motor resistors positioned in the duct' between the air propelling means and `the discharge opening thereof; supplementary electrically enerzimbie heating resistors situated withintheairductinsuchposition thtnllair lelvinz the discharge opening of the nir duct must plu thereover; e damper. said. damper adopted to clone or open the entrance to the duct from the outside atmosphere:v means to operate said damper. seid duct provided with a second dischme opening positioned beyond the traction motor resistors in the direction toward the discharge opening oi' the duct; s. damper adapted to close and open selectively the last-named opening to control discharge of air from the duct to the outside atmosphere and means to operate said l lest-named damper.

ROBERT J. PARSONS. 

